Tailoring the dielectric screening in WS2-graphene heterostructures

The environment contributes to the screening of Coulomb interactions in two-dimensional semiconductors. This can potentially be exploited to tailor material properties as well as for sensing applications. Here, we investigate the tuning of the band gap and the exciton binding energy in the two-dimensional semiconductor WS2 via the external dielectric screening. Embedding WS2 in van der Waals heterostructures with graphene and hBN spacers of thicknesses between one and 16 atomic layers, we experimentally determine both energies as a function of the WS2-to-graphene interlayer distance and the charge carrier density in graphene. We find that the modification to the band gap as well as the exciton binding energy are well described by a one-over-distance dependence, with a significant effect remaining at several nanometers distance, at which the two layers are electrically well isolated. This observation is explained by a screening arising from an image charge induced by the graphene layer. Furthermore, we find that the effectiveness of graphene in screening Coulomb interactions in nearby WS2 depends on its doping level and can therefore be controlled via the electric field effect. We determine that, at room temperature, it is modified by approximately 20% for charge carrier densities of 2 x 10(12) cm(-2).

Automated summary

The environment plays a role in screening Coulomb interactions in two-dimensional semiconductors, which can be used for material property manipulation and sensing applications. In this study, we investigate the tuning of band gap and exciton binding energy in two-dimensional semiconductor WS2 by external dielectric screening. By embedding WS2 in van der Waals heterostructures with graphene and hBN spacers of varying thickness, we experimentally determine the energies as a function of distance and charge carrier density. We find that the modification to the band gap and exciton binding energy can be described by a one-over-distance dependence, with a significant effect even at several nanometers distance.